Start by simplifying all complex terms (anything term that can be broken down into an easier thing to work with). 4^2 is equal to 4x4 or 16, and the square root of 25 is 5. Now we have an expression that looks like this:
16-25x2
Using PEMDAS, we continue simplifying by multiplying 5 and two together, and then subtracting this from 16.
